Include RPM packages in releases

Details

Description

CASSANDRA-13230 sets up docker builds for deb and rpm packages out of the cassandra-builds git repo. We should now be able to do builds in CI, at least for build testing of snapshot packages.

In order to include in releases, we may wish to set up bintray for RPMs in a redhat/ dir, similar to the current debian/ dir redirect from cassandra-dist, or start with direct downloads from cassandra-dist and see how it goes.